This invention relates to a power turbine unit comprising a turbine housing, an exhaust duct, a turbine wheel with blades positioned in said exhaust duct, a shaft rigidly connected to said turbine wheel and rotatably supported m said housing, and an oil sealing system comprising a sealing arrangement positioned in the vicinity of the turbine wheel for preventing oil from escaping from said turbine housing along said shaft to said exhaust duct. The invention also relates to an internal combustion engine comprising such a power turbine unit. The power turbine unit according to the invention can advantageously be provided to all types of internal combustion engines, in particular large combustion engines, such as in heavy trucks, buses and constructional vehicles.
It is known for example from document DE 10 2005 047 216 A1 to seal the turbine shaft by means of pressurised air. The pressurised air is supplied to a region of the shaft that is axially delimited by two sealing elements. This solution is relatively complex, and it requires reliable and constant supply of pressure controlled air from an air compressor, as well as two high performance sealing elements. There is thus a need for a simplified sealing arrangement fin a power turbine unit, where the above mentioned disadvantages are removed.
It is desirable to provide an inventive power turbine unit where the previously mentioned problems are at least partly avoided. The invention concerns, according to an aspect thereof, a power turbine unit comprising a turbine housing, an exhaust duct, a turbine wheel with blades positioned in said exhaust duct, a shaft rigidly connected to said turbine wheel and rotatably supported in said housing, and an oil sealing system comprising a sealing arrangement positioned in the vicinity of the turbine wheel for preventing oil from escaping from said turbine housing along said shaft to said exhaust duct.
An aspect of the invention is characterized in that said oil sealing system comprises a buffer gas duct that is arranged to supply exhaust gas from said exhaust duct to said sealing arrangement for pressurizing said sealing arrangement.
The inventive solution results, according to aspects thereof, in many advantages over the prior art. Most important, it does not require any pressurised air to be supplied from an external air compressor or the like. As a result, no active air flow and pressure control is required, no air supply tubes are required, and less pressurised air is required, thereby reducing fuel consumption and cost. The inventive solution, according to aspects thereof, is self-sustained and as such more reliable and allows simplified assembly of the engine.
Further advantages are achieved according to aspects thereof. For example, the buffer gas duct may be formed partly of an outer buffer gas duct wall separate from said housing. This design allows the outer buffer gas duct wall to operate at a higher temperature than the turbine housing temperature. The turbine housing has relatively good thermal connection to other parts of the engine in which the power turbine is arranged to be installed. For example, the turbine housing may be rigidly connected to a fluid coupling for transmitting the rotary power of the power turbine to for example an engine output shaft. This results in a cooling effect on the turbine housing. Furthermore, the lubricating oil within the engine also has a cooling effect on the turbine housing. When hot exhaust gas contacts the relatively cool turbine housing, soot and particles deposit on the cool surface and this may be a problem if the turbine housing forms a buffer gas duct wall. By forming the buffer gas duct partly of an outer buffer gas duct wall hat is separate from the turbine housing, the outer buffer gas duct wall may with proper installation attain a higher temperature than the turbine housing temperature such that less soot and particles of the exhaust flow will deposit on the surface of the outer buffer gas duct wall and more soot and particles will burn off when exhaust temperature is high.
Moreover, the buffer gas duct may be formed partly of an outer buffer gas duct wall and an inner buffer gas duct wall, each of which being separate from said housing. As described above, the separate inner and outer buffer gas duct walls allows higher duct wall temperature, thereby reducing soot and particles deposition on the inner walls of the buffer gas duct.
Furthermore, the buffer gas duct may be formed by at least an outer buffer as duct wall that is fastened to said housing by means of a fastener, or the buffer gas duct may be formed of said outer buffer gas duct wall and an inner buffer gas duct wall, each of which being fastened to said housing by means of a fastener. As described above, the inner and/or outer buffer gas ducts walls may result in higher temperature of the walls of the buffer gas duct, thereby reducing the trapped and contaminated inside of the buffer gas duct.
Furthermore, the outer buffer gas duct wall may form an inner wall of said exhaust duct. The dual function of the outer buffer has duct wall as buffer gas duct wall and exhaust gas wall results in a higher temperature of the outer buffer gas duct wall and allows simple and straightforward inlet of high pressure and high temperature exhaust has to the buffer gas duct for supply thereof to the sealing arrangement.
Furthermore, the inner and/or outer buffer gas duct wall may be formed of sheet metal. Sheet metal generally exhibits high thermal conductivity, high thermal form stability, and relatively cost-effective manufacturing processes.
Furthermore, the inner and/or outer buffer gas duct wall may be at least partly formed of an annular conical sleeve section that surrounds said shaft. The annular conical sleeve defines at least partly a buffer gas duct having a large flow area, such that internal fluid dynamic losses are reduced, and sufficient bailer gas flow is accomplished.
Furthermore, the buffer gas duct may be thermally insulated from said housing. Thereby the cooling effect of the housing, is reduced and the buffer gas duct walls may reach higher operating temperatures, and consequently reduced soot and particles deposition.
Furthermore, the thermal insulation may be partly formed by an air gap and/or insulation material having a low thermal conductivity, which thermal insulation is arranged between the buffer gas duct and said housing.
Furthermore, the thermal insulation may be partly realised by providing said fastener in at least one axial end region of said buffer gas duct, and specifically only in one axial end region of said buffer gas duct. The fasteners of the buffer gas duct potentially results in increased thermal coupling between the housing and buffer gas duct walls, thereby reducing the operating temperature of said walls. By providing fasteners in axial end regions, a minimum amount of fasteners is required to securely fasten the buffer gas duct walls to the housing.
Furthermore, said thermal insulation may be partly realised by insulation material provided between at least part of said fastener and said inner and/or outer buffer gas duct walls. This design further reduces the cooling effect of the housing.
Furthermore, said fastener may be engaged in a hole or recess in said inner and/or outer buffer gas duct walls. This design allows cost-effective manufacturing of the buffer gas duct walls.
Furthermore, said outer buffer gas duct wall may have a first section forming part of said exhaust duct, and a second section extending radially inwardly towards said shaft. This design allows the outer buffer gas duct wall itself to guide the exhaust gas directly to the sealing arrangement without the need for any intermediate gas guiding means, such as pipes etc.
Furthermore, said sealing arrangement may comprise a first sealing section and a second sealing section, said first sealing section being axially displaced from said second sealing section, and said buffer gas duct is arranged to supply exhaust gas to an annular cavity that is axially delimited by said first and second sealing sections. The first and second sealing sections are configured to deliver a flow of exhaust gas past the first sealing section and into the engine, but without feeding an excessive amount of high pressure exhaust into the engine. The flow of exhaust gas past the first sealing section and into the engine is caused by the pressure difference between the annular cavity of the sealing arrangement and the inside of the engine, i.e. the pressure within the crankcase housing, also referred to as engine blow-by pressure. When this pressure difference is positive, a flow of exhaust gas past the first sealing section will occur, thereby effectively preventing any leakage of oil out through the sealing arrangement. Too high flow is however negative since it requires increased crankcase ventilation. The second sealing section is preferably arranged to completely prevent exhaust gas from escaping the annular cavity past the second sealing section and out into the exhaust stream, but in practice such a flow of exhaust gas will nearly always occur.
Furthermore, said second sealing section is defined partly by said outer buffer gas duct wall.
Furthermore, said second sealing section is defined partly by at least one radial projection arranged on said shaft. A radial projection arranged on the shaft may in cooperation with an opposing counter-surface form a labyrinth seal that enables a sufficient sealing performance in a cost-effective and simple manner. Due to the lack additional separate external sealing rings, or the like, this solution is also particularly robust and maintenance-free.
Furthermore, at least one exhaust gas inlet may be provided in a wall of said exhaust duct for conveying exhaust gas from said exhaust duct into said buffer gas duct. This arrangement has the advantage of providing hot exhaust gas with sufficient pressure to the buffer gas duct without the need for additional components. Advantageously, the at least one exhaust gas inlet may be provided directly in the outer buffer gas duct wall. This simplifies manufacturing of the power turbine unit, and enables hot pressurised exhaust gas to directly enter the buffer gas duct upon passing through the exhaust gas inlet.
Furthermore, at least one exhaust gas inlet may be formed as a NACA inlet. This design allows good inlet flow of exhaust gas with low disturbance of the exhaust gas flow in the exhaust gas duct.
Furthermore, said exhaust duct may be a diffuser duct, and said at least one inlet may be arranged in a downstream region of said diffuser duct, where the exhaust gas static pressure is configured to be higher than in an upstream region of said diffuser duct. Increased exhaust gas static pressure means improved flow into the exhaust gas inlet in the exhaust gas duct, such that sufficient pressure may always be provided at the sealing arrangement to prevent oil leakage.
Furthermore, said at least one inlet may be arranged downstream of the turbine wheel in said exhaust duct. Arranging the inlet, downstream of the turbine wheel allows a shorter buffer gas duct; because the sealing arrangement is also arranged downstream the turbine wheel.
The invention also relates to an internal combustion engine comprising a turbo charger and a power turbine unit, wherein said power turbine unit is arranged downstream said turbo charger and connected to an engine crankshaft via fluid coupling and a gear train.